1. Field of the Technology
This invention relates to a wide-band wave plate made of multiple wave plate elements and a method of controlling the wide-band wave plate.
2. Description of the Related Art
Wave plates using the structured double refraction have been hard to be fabricated and reproduced because the structures are as large as their wavelengths and high aspect ratios are required to get generally-required phase differences (λ/4 and λ/2). Further, the structure of a wide-band property does not always have a high transmission efficiency at a structure height to get an optimum phase difference because the transmittance is dependent upon structure height.
In a conventional wave plate structure which combines two wave plates (A and B) with their main axes (a and b) matched together as shown in FIG. 5, an expected phase difference cannot be obtained if the wave plates (A and B) have production errors.
Patent Document 1 (shown below) discloses a polarization-axis-rotating laminated wave plate (retardation film) which laminates at least two wave plates of 60 to 300 nm (as the retardation value) with their slow axes set to a preset angle which is neither perpendicular nor parallel to each other. The invention of Patent Document 1 aims to make the wavelength range of the wave plate wider by shifting slow axes of the wave plates.
Patent Document 2 discloses a holographic optical element made of two relief-type gratings which are placed side by side at a predetermined relative angle between the grating grooves on the light axis. The phase difference of the optical element is controlled by adjusting the relative angle between the grating grooves of two relief-type gratings. However, this document does not consider any transmittance of optical elements.
Patent Document 1: Japanese Non-Examined Patent Publication H10-90521
Patent Document 2: Japanese Non-Examined Patent Publication 63-155107